The present invention relates to a flexible shaft coupling element and flexible couplings incorporating such element. The flexible shaft coupling element is in the form of a flexible sleeve-shaped body comprising an annular portion and two coupling receiving portions on opposing sleeve ends at either end of the annular portion. Each of the coupling receiving portions includes a plurality of axially extending ribs or teeth along at least a portion of the inner periphery of the sleeve-shaped body for slidably meshing with grooves in oppositely disposed hubs or end pieces. Such couplings are used to connect two rotating shafts which may be coupled to the end pieces. The flexible shaft coupling of the present invention is useful for accommodating misalignment of two shafts to be coupled together, and for providing a silently operating driving connection between the shafts by virtue of its flexible annular portion or band and the resiliency of its ribs or teeth.
Heretofore, flexible shaft couplings comprising a flexible load carrying band or annular portion and coupling receiving portions having axially extending ribs for engaging axially extending grooves on oppositely disposed hubs or end pieces were characterized in that such ribs typically possessed a trapezoidal profile or contour, and mated with complementary contoured grooves in the generally rigid end pieces. The ribs of such elements are characteristically elastomeric and the end pieces against which the ribs bear are characteristically formed of metal, resulting in a disproportionate amount of strain on the elastomeric ribs vis-a-vis the end piece grooves.
Improvements in the design of these coupling elements have generally been directed toward strengthening the load carrying band to withstand ever greater torsional loading. Because the load bearing capability of such load carrying bands has steadily increased as a result of such improvements, the elastomeric ribs have been required to bear ever-increasing torsional strain.
Flexible shaft coupling devices of the prior art thus generally exhibit a characteristic failure mode, consisting of the ripping or shearing-off of one or more of the teeth from the inner periphery of the sleeve body due to the effect of torsional stress or applied load. Typically, not just one of the teeth would be sheared off in this way, but the entire tooth profile would be sheared away from the much higher strength load carrying backing of the coupling element, leaving a smooth, empty sleeve-shaped shell in the area of one or both coupling receiving portions. Thus, despite the increased strength of prior art coupling element sleeve bodies, such elements generally experienced premature failure due to the effects of torsional loading on the teeth.
This failure mode is moreover particularly troublesome since such shearing-off of the teeth is not apparent from a view of the outer surface of the coupling. One cannot ascertain the levels of torque being transmitted or the proportion of useful life remaining in the coupling without first stopping the drive, removing the elastomeric sleeve, and then performing a visual inspection of the tooth portion of the coupling element. At minimum, this decreases production output and increases engineering costs. Worse yet, very often the first indication of failure may be the total destruction of the coupling element.